The Columbia Generating Station near Richland, WA, shut down about 1:30 p.m. on Monday, Energy Northwest spokesman John Dobken said.

Officials hope to restart the plant sometime this week, Dobken said.

The plant shut down after operators ended up alerted to problems with the system that uses water to cool heat exchangers and pumps, including those that control the power level of the reactor.

Energy Northwest said it seems a water system valve may not have been in the right position, but added an investigation is ongoing.

The last time the plant had an unplanned shutdown, known as a scram, was in November 2009, when there was a hydraulic fluid leak.

Mike Paoli, an Energy Northwest spokesman, said a decision on restarting the plant will occur after a thorough review of the event and when operators have confidence all systems can operate to standards.

“Scrams are not unusual events in the industry, but they are not what we like to see to meet our generation numbers,” Paoli said.

The nation has 99 operating nuclear reactors and they had more than 110 scrams in the last two years, he said.

The plant broke generation records in December and January, operating in January above its peak capacity factor, which is set at the maximum amount of electricity the plant can send to the power grid in the summer. It produces enough electricity to power a city about the size of Seattle.

The plant also had set a new record for the longest continuous operational run last year, operating for 683 days before shutting down for a planned biennial refueling and maintenance outage.

Energy Northwest is a consortium of 27 public power utilities that own the nuclear plant, located on the Hanford Nuclear Reservation.